This invention relates in general to electroformed belts, and in particular, to a process for electroforming metal belts.
Electroforming has been known for many years as a method for producing metal objects by passing an electric current through an electrolyte solution in which are immersed an anode and a cathode, in order to deposit a metal in the electrolyte solution onto either the anode or the cathode, thus forming an object.
U.S. Pat. No. 3,844,906 to Bailey et al. discloses a process for maintaining a continuous and stable aqueous nickel sulfamate electroforming solution adapted to form a relatively thin, ductile, seamless nickel belt. Nickel is electrolytically deposited from the solution onto a support mandrel. A nickel belt is recovered by cooling the nickel coated mandrel, effecting a parting of the nickel belt from the mandrel due to the different respective coefficients of thermal expansion. The process comprises establishing an electroforming zone comprising a nickel anode and a cathode comprising the support mandrel, the anode and cathode being separated by the nickel sulfamate solution maintained at a temperature of about 140.degree. to 160.degree. F. and having a current density therein ranging from about 200 to about 500 amps/ft.sup.2 ; imparting sufficient agitation to the solution to continuously expose the cathode to fresh solution; maintaining the solution within the electroforming zone at a stable equilibrium composition comprising nickel, halide and boric acid; electrolytically removing metallic and organic impurities from the solution upon removal from the electroforming zone; continuously charging to the solution about 1.0 to 2.0.times. 10.sup.-4 moles of a stress reducing agent per mole of nickel electrolytically deposited from the solution; passing the solution through a filtering zone to remove any solid impurities therefrom; cooling the solution sufficiently to maintain the temperature within the electroforming zone upon recycle thereto to about 140.degree. to 160.degree. F. at the current density in the electroforming zone; and recycling the solution to the electroforming zone.
U.S. Pat. No. 4,501,646 to Herbert discloses an electroforming process for forming hollow articles having a small cross-sectional area. In this patent, the electroforming process employs a cathode for the core mandrel having an electrically conductive, adhesive outer surface, an anode, and an electrolyte bath comprising a salt solution of the metals used for the electrodes. This patent discloses a belt having a thickness of at least about 30 .ANG. and stress-strain hysteresis of at least about 0.00015 in./in., and wherein a stress of between about 40,000 psi and about 80,000 psi is imparted to the cooled coating to permanently deform the coating and to render the length of the inner perimeter of the coating incapable of contracting to less than 0.04% greater than the length of the outer perimeter of the core mandrel after cooling. Any suitable metal capable of being deposited by electroforming and having a coefficient of expansion between about 6.times.10.sup.-6 to 10.times.10.sup.-6 in./in./.degree.F. may be used in the process. The '646 patent describes the use of this process for forming electrically conductive, flexible, seamless belts for use in an electrostatographic apparatus wherein the belt is fabricated by electrodepositing a metal onto a cylindrically shaped mandrel which is suspended in the electrolytic bath.
U.S. Pat. No. 4,664,758 to Grey discloses an electroforming process wherein, prior to electroforming, a uniform coating of an electrically conductive metal or metal alloy is applied to the core, the metal or metal alloy coating having a melting point and a surface tension less than the melting point and surface tension of the mandrel core. The coated mandrel core is immersed in an electroforming bath, and an electroformed metal belt having a melting point greater than the coating is deposited on the coating. The electroformed metal belt is removed from the mandrel core by heating the electroformed metal belt and/or the mandrel core to a temperature which is sufficient to melt the metal or metal alloy coating but insufficient to melt the electroformed metal belt and mandrel core. This permits the mandrel to be reused. This method also provides precise control of the electroformed coatings, by compensating for surface defects in the mandrel with the initial coating.
U.S. Pat. No. 4,787,961 to Rush discloses the use of an electroforming process for preparing a multilayered metal belt, wherein a tensile band set is formed from a plurality of separate looped endless bands in a nested and superimposed relation. The patent states that the bands are free to move relative to each other even though the spacing between adjacent bands is relatively small. These bands are formed in an apparatus comprising two rigid metallic anode plates and a cylindrical mandrel cathode. By rotating the mandrel by a motor and at the same time interconnecting the cathode and anodes to an electrical power supply, a certain amount of the material in the electrolyte bath is plated onto the surface to form a continuous or endless annular band which is readily removable from the surface and which comprises the innermost band of the band set. The electroforming process described in this patent forms a multilayered belt assembly by removing each belt from the electrolyte bath in order to coat it with a material to keep the belts from adhering to one another. Another belt is then formed around the previous belt. This requires many steps before achieving the final multilayered product.
Endless metal belts have been taught in the prior art for many purposes, including use with continuously variable transmissions.
U.S. Pat. No. 3,604,283 to Van Doorne discloses a continuously-variable transmission containing a driving mechanism which comprises a driving pulley with a V-shaped circumferential groove, a driven pulley with a V-shaped circumferential groove, and a flexible endless member having chamfered (beveled) flanks interconnecting and spanning the pulleys. The diameters of the pulleys automatically and steplessly can be varied with regard to each other in such a way that different transmission ratios can be obtained. The driving member described therein is a flexible endless member consisting of one or more layers of steel belts.
U.S. Pat. No. 4,661,089 to Cuypers discloses an endless metal belt for use with a continuously variable transmission which can be subjected to greater strains and which have a long service life. This patent describes an endless metal belt wherein the tensile stresses during operation are decreased by compressive stresses at the belt's edge zone. Permanent compressive stresses are incorporated in the belt's edge zones by shot peening or rolling. When such stresses are reduced, in particular by the tensile stresses caused by bending, the strain on the belts is not so great, and thus the likelihood of belt braking caused by hairline cracks occurring from the edges is decreased.
A continuously-variable transmission belt assembly ideally is comprised of a nest of several independent belts, designed in such a way that each belt has an outside diameter which is slightly less than the inside diameter of the next larger belt in the nest. This design permits the belts to share the load. However, it has not yet been disclosed how to produce a multilayer endless metal belt assembly with the necessary thin multiple belts that can be formed to the exacting tolerances required of a continuously-variable transmission belt and which are also capable of equal load sharing. In view of the great demand and many uses for endless metal belts, it is very desirable to find a less costly method of manufacturing these belts in such a manner that they will have the exacting tolerances needed.